The present invention, in some embodiments thereof, relates to additive manufacturing (AM), and more particularly, but not exclusively, to formulations useful for forming a support material in additive manufacturing such as three-dimensional inkjet printing, and to methods of additive manufacturing utilizing same.
Additive manufacturing (AM) is a technology enabling fabrication of arbitrarily shaped structures directly from computer data via additive formation steps (additive manufacturing; AM). The basic operation of any AM system consists of slicing a three-dimensional computer model into thin cross sections, translating the result into two-dimensional position data and feeding the data to control equipment which fabricates a three-dimensional structure in a layerwise manner.
Additive manufacturing entails many different approaches to the method of fabrication, including three-dimensional printing such as 3D inkjet printing, electron beam melting, stereolithography, selective laser sintering, laminated object manufacturing, fused deposition modeling and others.
Three-dimensional (3D) printing processes, for example, 3D inkjet printing, are being performed by a layer by layer inkjet deposition of building materials. Thus, a building material is dispensed from a dispensing head having a set of nozzles to deposit layers on a supporting structure. Depending on the building material, the layers may then be cured or solidified using a suitable device.
Various three-dimensional printing techniques exist and are disclosed in, e.g., U.S. Pat. Nos. 6,259,962, 6,569,373, 6,658,314, 6,850,334, 6,863,859, 7,183,335, 7,209,797, 7,225,045, 7,300,619, and 7,500,846 and U.S. Patent Application having Publication No. 20130073068, all by the same Assignee.
During the additive manufacturing (AM) process, the building material may include “model material” (also known as “object material” or “modeling material”), which is deposited to produce the desired object, and frequently, another material (“support material” or “supporting material”) is used to provide temporary support to the object as it is being built. The other material is referred to herein and in the art as “support material” or “supporting material”, and is used to support specific areas of the object during building and for assuring adequate vertical placement of subsequent object layers. For example, in cases where objects include overhanging features or shapes, e.g. curved geometries, negative angles, voids, and the like, objects are typically constructed using adjacent support constructions, which are used during the printing and then subsequently removed in order to reveal the final shape of the fabricated object.
The modeling material and the supporting material may be initially liquid and subsequently hardened to form the required layer shape. The hardening process may be performed by a variety of methods, such as UV curing, phase change, crystallization, drying, etc. In all cases, the support material is deposited in proximity of the modeling material, enabling the formation of complex object geometries and filling of object voids. In such cases, the removal of the hardened support material is liable to be difficult and time consuming, and may damage the formed object.
When using currently available commercial print heads, such as ink-jet printing heads, the support material should have a relatively low viscosity (about 10-20 cPs) at the working, i.e., jetting, temperature, such that it can be jetted. Further, the support material should harden rapidly in order to allow building of subsequent layers. Additionally, the hardened support material should have sufficient mechanical strength for holding the model material in place, and low distortion for avoiding geometrical defects.
Examples of materials that can be used as supporting materials are phase change materials, with wax being a non-limiting example. At an appropriately high temperature these materials melt and thus permit support removal when in the liquid state. One of the drawbacks of such phase change is that the temperature required for melting the supporting material may also cause deformation of the model, and hence of the object structure.
Known methods for removal of support materials include mechanical impact (applied by a tool or water-jet), as well as chemical methods, such as dissolution in a solvent, with or without heating. The mechanical methods, however, are labor intensive and are unsuited for small intricate parts.
For dissolving the support materials, the fabricated object is often immersed in water or in a solvent that is capable of dissolving the support materials. In many cases, however, the support removal process may involve hazardous materials, manual labor and/or special equipment requiring trained personnel, protective clothing and expensive waste disposal. In addition, the dissolution process is usually limited by diffusion kinetics and may require very long periods of time, especially when the support constructions are large and bulky. Furthermore, post-processing may be necessary to remove traces of a ‘mix layer’ on object surfaces. The term “mix layer” refers to a residual layer of mixed hardened model and support materials formed at the interface between the two materials on the surfaces of the object being fabricated, by model and support materials mixing into each other at the interface between them.
Additionally, methods requiring high temperatures during support removal may be problematic since there are model materials that are temperature-sensitive, such as waxes and certain flexible materials. Both mechanical and dissolution methods for removal of support materials are especially problematic for use in an office environment, where ease-of-use, cleanliness and environmental safety are major considerations.
Water-soluble materials for 3D building have been previously described. For example, U.S. Pat. No. 6,228,923 describes a water soluble thermoplastic polymer—Poly(2-ethyl-2-oxazoline)—for use as a support material in a 3D building process involving high pressure and high temperature extrusion of ribbons of selected materials onto a plate.
A water-containing support material comprising a fusible crystal hydrate is described in U.S. Pat. No. 7,255,825. Fusible crystal hydrates undergo a phase change from solid to liquid (i.e. melt) usually at higher than ambient temperature (typically between 20° C. and 120° C. depending upon the substance). Typically, upon melting, fusible crystal hydrates turn into aqueous solutions of the salts from which they are formed. The water content in these solutions is typically high enough to make the solutions suitable for jetting from a thermal ink-jet printhead. The melting process is reversible and material dispensed in a liquid state readily solidifies upon cooling.
Water-soluble compositions suitable for support in building a 3D object are described, for example, in U.S. Pat. Nos. 7,479,510, 7,183,335 and 6,569,373, all to the present Assignee. Generally, the compositions disclosed in these patents comprise at least one UV curable (reactive) component, e.g., an acrylic component, at least one non-UV curable component, e.g. a polyol or glycol component, and a photoinitiator. After irradiation, these compositions provide a semi-solid or gel-like material capable of dissolving or swelling upon exposure to water, to an alkaline or acidic solution or to a water detergent solution.
Besides swelling, another characteristic of such a support material may be the ability to break down during exposure to water, to an alkaline or acidic solution or to a water detergent solution because the support material is made of hydrophilic components. During the swelling process, internal forces cause fractures and breakdown of the cured support. In addition, the support material can contain a substance that liberates bubbles upon exposure to water, e.g. sodium bicarbonate, which transforms into CO2 when in contact with an acidic solution. The bubbles aid in the process of removal of support from the model.